The invention relates to the field of optoelectronics and in particular to semiconductor radiation emitters and to photoreceivers.
Most optoelectronic devices based on semiconductors have p-n junctions integrated into their active parts.
This is for example the case with LEDs (light-emitting diodes). Thus, at the contact of two, type n and type p, semiconductors, the charge carriers of each type combine in the active zone, emitting photons. The active zone is often composed of one or more quantum wells which provide a high luminescence efficiency and enable the emission wavelength to be adjusted, by controlling their composition and their thickness.
N-type or p-type semiconductors may be obtained by intrinsic doping, conventionally by stoichiometric defects.
N-type and p-type semiconductors may also be obtained by extrinsic dopants that are introduced into the matrix, either during growth of the materials or after their growth, by a technique such as diffusion or ion implantation. However, it should be noted that, during growth on a heterosubstrate, there is diffusion of the light atoms from the substrate (aluminium atoms in the case of an Al2O3 substrate) and therefore extrinsic doping, but there are often stoichiometric defects (for example oxygen vacancies), and therefore also intrinsic doping.
Thus, document WO 2004/088755 may be cited, which describes a nanostructure of the nanowire type incorporating p-n junctions. In one of the embodiments described, a nanowire is formed on a substrate and then two layers of a polymer material are deposited in succession on the substrate. The first polymer layer has a given concentration of dopants of a first type (for example, donors), the second layer comprising dopants of a second type (acceptors). The structure then undergoes a suitable heat treatment so as to allow the dopants to diffuse from each of the two layers into two successive portions of the nanowire. This makes it possible to create a p-n junction between the two portions.
Thus, the above document describes so-called extrinsic doping techniques in which more precisely a first doping of a first type and a second doping of a second type are carried out.
Throughout the present Application, it should be understood that “extrinsic doping” of a matrix means doping carried out by dopants differing in nature from said matrix that are introduced into said matrix during the growth or come from another material.
These semiconductor doping techniques have certain drawbacks.
To be specific, although extrinsic doping is for the present time well understood and controlled in certain semiconductors, such as for example silicon (Si) or gallium arsenide (GaAs), this is not the case for other semiconductors, such as gallium nitride (GaN) or zinc oxide (ZnO). In the latter case, the doping is sometimes difficult or requires heat treatment or else complex processes. For example, techniques for the p-type doping of ZnO have not yet been developed. In addition, for certain semiconductors, doping is sometimes unstable, or even impossible.
To alleviate these drawbacks, processes have therefore been proposed for producing a p-n junction in a nanostructure using a single type of doping.
These processes are based on a structure having a metal layer surrounded by dielectric layers in order to avoid electric charge transfer to the outside of the metal layer, the p-n junction of the nanostructure being produced by biasing the metal layer. Typically, such a structure is of the transistor type that can be produced with a gate, the bias of which modifies the type of conductivity of the channel beneath said gate, and is then in an on-state or an off-state depending on the gate bias.
However, the structure is relatively complicated insofar as it requires the deposition of at least three successive layers around the nanowire. Moreover, this process requires means for biasing the metal element so as to produce the p-n junction in the nanostructure.